1. Field of the Invention
The present invention relates to an image pickup apparatus such as a digital camera or a video,
2. Description of the Related Art
Previously, there has been an image pickup element that has a phase difference detection function of an object image to achieve a high-speed phase difference AF without using a dedicated AF sensor. Japanese Patent Laid-Open No. 2000292686 discloses pixels of an image pickup element to which a pupil division function is given by decentering a sensitivity region of a light receiving portion with respect to an optical axis of an on-chip microlens. These pixels are used a focus detection pixels and are arranged between imaging pixels at a predetermined interval to perform phase difference focus detection. Japanese Patent Laid-Open No. 2008-085738 discloses an image pickup apparatus that adds image data of focus detection pixels stored by a plurality of past readouts to perform focus detection calculation in order to satisfy both a refresh operation with a short period and focus detection for a low-luminance object.
The image pickup apparatus disclosed in Japanese Patent Laid-Open No. 2008-085738 stores image data of the focus detection pixel in each frame and performs the focus detection calculation based on image data obtained by adding the image data of the focus detection pixel stored by the plurality of past readouts. However, when a stop value, a focal length, or the like changes during obtaining the image data of the focus detection pixel, a shift of a defocus amount that is to be converted from an image shift amount is generated.